Genetic models for studying localized cell suicide that halt the spread of pathogen infection and immune response activation in plants include Arabidopsis accelerated-cell-death 11 mutant (acd11). In this mutant, sphingolipid homeostasis is disrupted via depletion of ACD11, a lipid transfer protein that is specific for ceramide 1-phosphate (C1P) and phyto-C1P. The C1P binding site in ACD11 and in human ceramide-1-phosphate transfer protein (CPTP) is surrounded by cationic residues. Here, we investigated the functional regulation of ACD11 and CPTP by anionic phosphoglycerides and found that 1-palmitoyl-2-oleoyl-phosphatidic acid or 1-palmitoyl-2-oleoyl-phosphatidylglycerol (≤15 mol %) in C1P source vesicles depressed C1P intermembrane transfer. By contrast, replacement with 1-palmitoyl-2-oleoyl-phosphatidylserine stimulated C1P transfer by ACD11 and CPTP. Notably, "soluble" phosphatidylserine (dihexanoyl-phosphatidylserine) failed to stimulate C1P transfer. Also, none of the anionic phosphoglycerides affected transfer action by human glycolipid lipid transfer protein (GLTP), which is glycolipid-specific and has few cationic residues near its glycolipid binding site. These findings provide the first evidence for a potential phosphoglyceride headgroup-specific regulatory interaction site(s) existing on the surface of any GLTP-fold and delineate new differences between GLTP superfamily members that are specific for C1P versus glycolipid.
Bibliographical noteFunding Information:
This work was supported in whole or part by NIGMS, National Institutes of Health (NIH), Grant GM45928 and NHLBI, NIH, Grants HL125353 and NCI CA121493; Russian Foundation for Basic Research Grant 015-04-07415; Danish Strategic Research Council Grant 09-067148; the Abby Rockefeller Mauze Trust; and the Maloris and Hormel Foundations. Portions of this work were presented at the 2015 American Chemical Society and 2015 American Society for Biochemistry and Molecular Biology Annual Meetings. The authors declare that they have no conflicts of interest with the contents of this article. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. We thank Helen Pike for expressing and purifying CPTP.